A vehicle engine at idle is operating at a minimum speed to generate enough power to operate its ancillaries, such as the water pump, alternator, and other accessories, such as air conditioning, but may not generate enough power to effectively move the vehicle.
An idling vehicle is a vehicle that has its engine running while parked or not in use. Often a driver deliberately allows the engine to idle in order to “warm up” the car, do an errand, wait for someone while retaining personal comfort, listen to the radio, or park illegally.
Currently, effort is being made to reduce the amount of time vehicle engines spend idling. Many states have implemented regulations limiting the number of minutes a vehicle can idle. Fines ranging from a few hundred dollars (U.S.) to thousands of dollars (U.S.) can be incurred for failing to follow the idling regulations. Indeed, the United States Environmental Protection Agency (EPA) has compiled a list of over 30 states having state, county and/or local anti-idling regulations. In addition, many organizations, such as American Transportation Research Institute (ATRI) provide a compendium of idling regulations. The basis for implementing these regulations stems from fuel economy and emissions concerns.
However, in addition to the environmental impact of excessive idling, excessive idling can contribute to the damage of certain engine components, including cylinders, spark plugs, and exhaust systems.
An idling engine is not operating at its peak temperature, which means that fuel does not undergo complete combustion. This leaves fuel residue that can condense on cylinder walls, where they can contaminate the oil and damage parts of the engine. For example, fuel residues are often deposited on spark plugs. As idling time increases, the average temperature of the spark plug drops. This can cause the plug to get dirty more quickly, which may increase fuel consumption. Excessive idling also lets water condense in the vehicle's exhaust, which can lead to corrosion and reduce the life of the exhaust system.
Accordingly, research continues to be conducted to provide start-stop systems to shut off a vehicle engine when it would otherwise be idling.